1. Louisiana State University, Section of Pulmonary/Critical Care Medicine, New Orleans, Louisiana
2. University of Washington, Division of Pulmonary/Critical Care Medicine, Seattle, Washington
3. University of Pittsburgh, Division of Pulmonary/Critical Care Medicine, Pittsburgh, Pennsylvania
4. Massachusetts General Hospital, Biostatistics Center, Department of Medicine, Boston, Massachusetts
5. University of Washington, Department of Epidemiology, Seattle, Washington
6. Massachusetts General Hospital, Division of Pulmonary/Critical Care Medicine, Boston, Massachusetts; and
7. Vanderbilt University, Division of Pulmonary/Critical Care, Nashville, Tennessee